This invention relates to voltage control systems. It has particular application to the control of voltage by a consumer supplied with power from a utility system. The invention is also directed to providing a variable transformer in which a moving core structure is used to achieve step-free voltage control in response to changing input voltages, and in which output voltage is made to change linearly with respect to time.
Power control systems are known. Many involve some form of load shedding, which is undesirable, since it requires removal of one or more devices from use. The present invention is directed to a power control system using voltage control as a principal factor, but also utilizes load shedding or load reduction as desired.
In the past, much publicity has been given to the "brown-out" condition, in which the voltage supplied by a utility to a consumer falls below a desired level. Little attention has been given to the supplying of excessive voltage by a utility. Since a consumer pays for electricity upon the basis of power consumed, i.e., the product of voltage and current and phase angle and since current and power usually increase when voltage increases, excessive power is consumed and paid for by a consumer when voltage increases beyond a desired level. The present invention is directed toward a system for handling conditions of excessive voltage, as well as insufficient voltage, i.e., to supply correct voltage in response to varying input voltage conditions.
The present invention utilizes a variable transformer as a control device. In the past, variable transformers for voltage control purposes have generally involved moving coils or changing/sliding electrical contacts. Both arrangements are undesirable, since electrical conductors are being moved or switched in and out of a circuit, accompanied by arcing, noise, losses, wear, and other problems. The present invention utilizes a transformer structure involving fixed coils, and no moving contacts. Instead, a part of the magnetic core structure is movable, to change the magnetic flux in the transformer that links the windings in the transformer, so as to achieve voltage control. Although movable transformer core structures have been utilized in the past, most have been for manual operation and not for automatic control as in the present invention. Although it has been proposed before to sense voltage and to control the position of a movable core structure in response thereto, the control mechanism has been spring biased or otherwise relatively freely movable, rendering it unsuitable for use in systems involving large currents, in which the magnetic forces generated are such as to cause movement of the movable core structure to a rest position. In the present invention, a movable core structure is locked in position following any adjustment.
Additionally, the present invention utilizes a non-linear movement of the movable core structure, so as to achieve linear changes in voltage over time. In particular, as the movable core structure moves away from a position adjacent to a pole piece, increasing an air gap, the magnetic flux linking these two members would normally sharply decrease, causing an abrupt and sharp voltage change. In the present invention, the movable core structure is made to move relatively slowly when the increasing air gap is encountered, thereby to eliminate this undesirable effect.
The invention will be more completely understood by reference to the following detailed description of presently preferred embodiments thereof.